1. Field of the Invention
The present invention generally relates to telemetry receivers used for monitoring and testing telemetry equipment and, more particularly, to multilingual code receivers which are capable of recognizing certain incompatible code formats and correctly decoding received data.
2. Description of the Prior Art
A recent development in the operation of railroad equipment has been the elimination of cabooses from freight trains. The caboose, as the last car in the train, was provided with a gauge to monitor the brake pipe air pressure. It was the job of the brakeman riding in the caboose to notify the engineer in the locomotive cab on a periodic or as required basis the status of the brake pipe air pressure at the end of the train. This was accomplished by a voice radio system which communicated between the caboose and the locomotive cab and allowed the brakeman to talk to the engineer.
The caboose is being replaced with telemetry equipment in the form of a battery powered monitoring and transmitter package which is mounted on the coupler of the last car of the train and a receiver mounted in the locomotive cab. The monitoring and transmitter package periodically measures and transmits encoded data on not only brake pipe air pressure, but also on the battery condition and other conditions such as motion of the last car in the train. The monitoring and transmitter package is required by Federal regulation to having a flashing light of specified intensity and beam pattern, and data relating to the condition and operation of this light might also be transmitted to the telemetry receiver in the locomotive cab. In short, this end of train telemetry equipment has the capability of providing the engineer with more information on the conditions at the rear of the train with more accuracy and reliability than a brakeman riding in a caboose whose attention might be diverted at a critical time. Moreover, the telemetry receiver is typically connected to data processing circuitry which can filter the data, displaying only that data the engineer needs to see and providing a timely alert to the engineer when an emergency condition is detected.
An example of an end of train telelmetry system such as described above is disclosed in U.S. Pat. No. 4,487,060 to Pomeroy. However, the leading exponent for the development and standardization of end of train telemetry systems has been the Association of American Railroads, hereinafter the AAR. The work of the AAR has been reported from time to time in various publications early examples of which are the TTD Post-Conference Proceedings, "Enhancing Train Operations Through On-Board Processing: The Advanced Locomotive Cab Instrumentaion System", by Ambrose, Kiger and Patel, Nov. 27 to 29, 1979, The Palmer House, Chicago, Ill., pp. 195 to 206, and Annual Proceedings of the Railway Fuel and Operating Officers Association, Inc., 1981: transcript of presentation by Steve Kiger, Consultant of the AAR, pp. 177 to 180 and 182 to 186.
Among the standards developed and promulgated by the AAR are the radio frequency specifications, encoding and data format of the telemetry transmissions. These have evolved over a period of years, but they were not without competing private standards developed by vendors of telemetry equipment. This has meant that equipment from various vendors have not been compatible. This has become a serious problem for some railroads which have purchased from more than one vendor, and can be a problem in any major rail depot where equipment from several vendors may be installed on different trains.
On the one hand, it would be desirable for a railroad to have test receiver equipment which can be used by railroad personnel to monitor transmissions from telemetry transmitters to assist them in testing and evaluation of the transmitters in their maintenance and repair operations. This has generally required the design and manufacture of different receivers for each different vendor source of telemetry equipment. The manipulation of more than one receiver in a laboratory is bothersome, but in the field the job becomes almost impossible creating many chances for error. On the other hand, railroads desire standardization of equipment for efficient operation. There has thus arisen a strong demand that the telemetry equipment can be "mixed-and-matched"; that is, the receiver in a controlling locomotive of a train will respond to the transmissions of a telemetry transmitter attached to the last car of the train no matter what the vendor source. Obviously, one way to accomplish this is to conform to the AAR standards. Unfortunately, there is now a large installed base of incompatible telemetry equipment from different vendors which does not conform to the AAR standards.